LITTLE ROCK, Ark. (Reuters) - Arkansas has said it will appeal a court ruling that bars the U.S. state's use of a lethal injection drug and effectively puts a stop to its plans to execute eight prisoners in 11 days.

A state circuit judge issued the temporary restraining order on Wednesday after the U.S. pharmaceutical firm McKesson Medical-Surgical Inc accused the state of obtaining the muscle relaxant pancuronium bromide under false pretences.

The company, a unit of McKesson Corp, said it would not have sold the drug to the Arkansas prison system had it known it would be used in executions, and is demanding the drug is either returned or confiscated.

The ruling delivered a further setback for the state, which last carried out an execution a dozen years ago and contends it must act quickly because its supply of another of the three drugs used in the lethal mix expires at the end of April.

A spokesman for State Attorney General Leslie Rutledge, a Republican, said she would appeal the ruling before the state's Supreme Court.

The execution of eight death row inmates would be the most by any U.S. state in such a short period since the death penalty was reinstated in 1976.

Arkansas officials have said they cannot obtain the drug from any other source, and have acknowledged in court papers that should McKesson prevail, all pending executions would be blocked.

Governor Asa Hutchinson said he was "both surprised and disappointed" by the latest legal delays.

The state had originally planned to execute eight death row inmates in four pairs in a span of 11 days, starting on April 17 and ending on April 27.

However, amid a flurry of legal challenges, four of the condemned prisoners have won stays of execution. Arkansas's Supreme Court issued the latest of those reprieves, for condemned killer Stacey Johnson, minutes before the lower-court ruling on McKesson's request.

Johnson was convicted of the 1993 murder and sexual assault of Carol Heath. Prosecutors said he beat, strangled and slit Heath's throat while her 6-year-old daughter watched. Judges sent Johnson's case back to the trial court to allow for new DNA evidence.

An appeal of Johnson's stay of execution was undecided, the attorney general's spokesman said.

Also still pending before the U.S. Supreme Court is an appeal by all eight prisoners contending that the compressed execution schedule increases the likelihood of a botched lethal injection. A federal appeals court had rejected their arguments.

Arkansas' death penalty push comes after the number of U.S. executions fell to a quarter-century low in 2016. (For a graphic on the number and method of U.S. executions, see: http://tmsnrt.rs/26wAN2v)